More engine API work

UIXrender/Interop/Drawing/Color.cs

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+using System.Runtime.InteropServices;
+
+namespace Microsoft.Iris.Render.Interop.Drawing;
+
+// Bit-for-bit mirror of Microsoft.Iris.Drawing.Color (UIX/Microsoft/Iris/Drawing/Color.cs)
+// -- a single packed 0xAARRGGBB uint, not four separate byte fields.
+[StructLayout(LayoutKind.Sequential)]
+public struct Color
+{
+    public uint value;
+
+    public Color(uint value) => this.value = value;
+
+    public byte A => (byte)(value >> 24);
+    public byte R => (byte)(value >> 16);
+    public byte G => (byte)(value >> 8);
+    public byte B => (byte)value;
+
+    public static Color FromArgb(byte a, byte r, byte g, byte b) =>
+        new((uint)((a << 24) | (r << 16) | (g << 8) | b));
+}

UIXrender/Interop/Drawing/ColorF.cs

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+using System.Runtime.InteropServices;
+
+namespace Microsoft.Iris.Render.Interop.Drawing;
+
+// Bit-for-bit mirror of Microsoft.Iris.Render.ColorF (UIX.RenderApi/Microsoft/Iris/Render/ColorF.cs).
+[StructLayout(LayoutKind.Sequential)]
+public struct ColorF
+{
+    public float a;
+    public float r;
+    public float g;
+    public float b;
+}

UIXrender/Interop/Drawing/Point.cs

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+using System.Runtime.InteropServices;
+
+namespace Microsoft.Iris.Render.Interop.Drawing;
+
+// Bit-for-bit mirror of Microsoft.Iris.Render.Point (UIX.RenderApi/Microsoft/Iris/Render/Point.cs).
+[StructLayout(LayoutKind.Sequential)]
+public struct Point
+{
+    public int x;
+    public int y;
+}

UIXrender/Interop/Drawing/Rectangle.cs

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+using System.Runtime.InteropServices;
+
+namespace Microsoft.Iris.Render.Interop.Drawing;
+
+// Bit-for-bit mirror of Microsoft.Iris.Render.Rectangle (UIX.RenderApi/Microsoft/Iris/Render/Rectangle.cs).
+[StructLayout(LayoutKind.Sequential)]
+public struct Rectangle
+{
+    public int x;
+    public int y;
+    public int width;
+    public int height;
+}
+
+// Bit-for-bit mirror of Microsoft.Iris.RenderAPI.Drawing.RectangleF
+// (UIX/Microsoft/Iris/RenderAPI/Drawing/RectangleF.cs).
+[StructLayout(LayoutKind.Sequential)]
+public struct RectangleF
+{
+    public float x;
+    public float y;
+    public float width;
+    public float height;
+}

UIXrender/Interop/Drawing/Size.cs

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+using System.Runtime.InteropServices;
+
+namespace Microsoft.Iris.Render.Interop.Drawing;
+
+// Bit-for-bit mirror of Microsoft.Iris.Render.Size (UIX.RenderApi/Microsoft/Iris/Render/Size.cs).
+[StructLayout(LayoutKind.Sequential)]
+public struct Size
+{
+    public int width;
+    public int height;
+
+    public Size(int width, int height)
+    {
+        this.width = width;
+        this.height = height;
+    }
+}

UIXrender/Interop/Drawing/SizeF.cs

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+using System.Runtime.InteropServices;
+
+namespace Microsoft.Iris.Render.Interop.Drawing;
+
+// Bit-for-bit mirror of Microsoft.Iris.RenderAPI.Drawing.SizeF (UIX/Microsoft/Iris/RenderAPI/Drawing/SizeF.cs).
+[StructLayout(LayoutKind.Sequential)]
+public struct SizeF
+{
+    public float width;
+    public float height;
+}